Background

Few estimates of the fraction of cases of breast cancer attributable to recognized risk factors have been published.

All estimates are based on selected groups, making their generalizability to the U.S. population uncertain.

Purpose

Our goal was to estimate the fraction of breast cancer cases in the United States attributable to well-established risk factors (i.e., later age at first birth, nulliparity, higher family income, and first-degree family history of breast cancer), using data from the first National Health and Nutrition Examination Survey (NHANES I) Epidemiologic Follow-up Study (NHEFS), the survey and follow-up of a probability sample of the U.S. population.

Methods

From a cohort of 7508 female participants surveyed in the early 1970s, and followed up between 1982 and 1984 and again in 1987,193 breast cancer cases were accrued for study.

We calculated incidence rates, relative risks (RRs), and population attributable risks (PARs) for breast cancer risk factors and extended our results to the U.S. female population by using sample weights from the NHANES I survey.

Results

Our PAR estimates suggest that later age at first birth and nulliparity accounted for a large fraction of U.S. breast cancer cases, 29.5% (95% confidence interval [CI]=5.6% - 53.3%) ; higher income contributed 18.9% (95% CI=-4.3% to 42.1%), and family history of breast cancer accounted for 9.1% (95% CI=3.0% - 15.2%). Taken together, these well-established risk...